<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    var sum = 0;
    for (var i = 1; i <= 100; i++) {
      sum += i;
    }
    alert('1-100的和为' + sum);
  </script>
</body>

</html>